Speed change devices for bicycles and similar vehicles are known some of these are fixed to the frame on or near the axle of the rear wheel. These speed change devices generally comprise a chain-guide system having one or more wheels with which the chain of the bicycle is engaged. By transversely displacing the chain-guide with its wheel, one can engage the chain as desired on one of the pinions of a free wheel cluster on the rear wheel of the bicycle.
This transverse displacement is remotely controlled by the cyclist by a lever or control button, most often but not exclusively, through the intermediary of a flexible cable system. To this effect, the chain-guide with its wheel can be carried by a system having a deformable articulated parallelogram which is constituted by levers pivoted to an upper support and to a lower support. The latter carries the chain-guide with its wheels by an elastic pivotal mounting of the chain-guide in order to constantly retain the necessary tension in the chain for proper operation.
It is known that it is difficult for the cyclist to control the transverse displacement of the chain-guide in a manner to align, with the required precision for proper operation, the chain and the teeth of the pinion corresponding to the selected speed. Frequently, the cyclist hunts for and passes the speed that he wants to engage. Then, the chain is not correctly aligned with the teeth of the pinion. There is thus produced friction and wear. In brief, the rider does not feel the correct transverse positions of passage of the speeds for each speed. The search for the correct position can, moreover, dangerously distract his attention.
Devices have been proposed for selecting the speeds which devices have serious disadvantages due either to their complexity and their cost or because they do not effect initial adjustment with respect to the teeth of the first pinion or by their unpleasing geometry and providing projecting members constituting dangerous points of contact.